Pressure transducers are used in a variety of industries and applications. They are used in manned and unmanned underwater vehicles to measure depth. They are used in aircraft to measure altitude and to monitor pressure in the compression stages of jet engines. Additionally, hydraulic and pneumatic control systems use pressure transducers for pressure control. The single largest user of pressure transducers is the automotive industry which uses transducers to monitor engine intake manifold pressure in order to control electronic fuel injection systems and to determine shift points for automatic transmissions.
Pressure transducers are available in a variety of types. Among the most commonly used pressure transducers are bellows type transducers, spring/diaphragm type transducers and diaphragm/strain gauge type transducers. Bellows type transducers are widely used in applications such as barometers and aircraft altimeters. On the other hand, because of the inability of the bellows to handle moderate to high pressures, this type of transducer is limited to low pressure applications.
Spring/diaphragm transducers are commonly used in applications such as oxygen regulators. Spring/diaphragm transducers, however, have the drawback that they are inherently inaccurate because the spring and the diaphragm will fatigue over time. As the parts fatigue, the transducer must often be adjusted and calibrated to compensate for the changes in the materials.
Diaphragm/strain gauge transducers, while commonly used for high pressure applications such as torpedoes, still have several drawbacks. Since the total deflection in this type strain gauge may be very small, often measured in microns, precision machining and assembly is required. Often these devices have a limited range of use and mechanical stops must be used to prevent failures when exposed to pressures outside the allowable range. As a result of this limited range, multiple transducers having different ranges must often be used. In the design of diaphragm/strain gauge transducers, great care must be taken in the selection of materials to ensure that dissimilar materials having different temperature coefficients don't distort the diaphragm when the device is exposed to varying temperatures during operation. Moreover, the resistors in the strain gauge must be temperature compensated as well. Still further, care must be taken when assembling a diaphragm/strain gauge type transducer to minimize machining, welding and bonding stresses. This is necessary because these stresses, will relax over time and appear during operation as long term stability problems or drift. As a result of the foregoing, diaphragm/strain gage type transducers are relatively expensive.
The foregoing transducers universally rely on physical deformation of a mechanical part to monitor pressure. Over time all will need adjustment because of fatigue stresses and strains in the deforming member. This presents its own problem because most pressure transducers must be removed from their installed positions for testing and calibration. Another problem affecting all the above transducers, and briefly touched upon, above is that temperature affects their structural components and therefore their performance. Finally, the foregoing mechanical pressure transducers only approximate linearity and are subject to pressure bias offset if stressed beyond their design limit. These problems are the result of the incomplete or imperfect elasticity of the deforming mechanical component.
In light of the above it is an object of the present invention to provide a pressure transducer which is compact and easy to use. It is another object of the present invention to provide a pressure transducer which is able to detect small variations in pressure over wide range of pressures. It is still another object of the present invention to provide a pressure transducer which is reliable and accurate. Yet another object of the present invention is to provide a pressure transducer which is operationally rugged. And yet another object is to provide a pressure transducer which is not affected by operating temperatures or residual manufacturing or assembly stresses. It is another object of the present invention to provide a fluid pressure transducer having long-term stability. Yet another object of the present invention is to provide a pressure transducer which is relatively easy to manufacture and which is relatively economical.